[cabfpub] Pre-Ballot 164 - Certificate Serial Number Entropy

Ryan Sleevi sleevi at google.com
Thu Apr 28 16:07:58 UTC 2016

On Thu, Apr 28, 2016 at 5:16 AM, Eneli Kirme <Eneli.Kirme at sk.ee> wrote:

> Hi,
> The current requirement was part of root program conditions already before
> first version of BR-s were published and could be taken as a requirement
> while developing or purchasing the CA software.

Actually, at the time the BRs were published, the requirement was 64 bits.
The BRs were looser (to 20 bits) than what Microsoft was requiring.

> As the vendor claimed compliance, we believe to be compliant.
> Changing to 64 bits may or may not make a difference - we have to check
> with the vendor. Adding some other restrictions on the types of acceptable
> RNGs is another change in requirements that may or may not make a
> difference.
> We also have to check with the auditors about what evidence they would
> like to see to believe that long enough seemingly random number comes from
> an acceptable source.
> But the question is more general - to which level you expect a CA to have
> control over the software it is using and to which level auditors should
> have access to it?

The expectation is that all CAs will be following the latest-published BRs,
per Section 2.2 of the BRs, specifically:

[Name of CA] conforms to the current version of the Baseline Requirements
for the Issuance and Management of Publicly‐Trusted Certificates published
at http://www.cabforum.org. In the event of any inconsistency between this
document and those Requirements, those Requirements take precedence over
this document.

To the extent a given CA has concerns about the BRs, such as the timing of
the deployment of updated software, that's useful information to bring
forward during the discussion of the proposed changes, and may inform the
voting on the ballot. But once a ballot has passed, the expectation is that
the CA will adopt it operationally "immediately", even if the audit
criteria for it is developed, and the audit expectation of compliance is
not enforced until the audit criteria are adopted.

This was discussed during the Scottsdale F2F as understanding when ballots
come into effect - when the consensus about the understanding that the
above clause represents an expectation to adopt immediately. That naturally
follows that CAs should be prepared to adopt the Ballots as they're
published, or their effective date, or to understand what challenges might
exist to prevent that.

That said, if there's concern about timing, arguably it's useful to know
concretely what the timing is.
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